Jhinhwan Lee - Korea Advanced Institute of Science and Technology

Description

Controlling iron-basedsuperconductivity with spin currents

Jhinhwan Lee

Department of Physics,Korea Advanced Institute of Science and Technology, Republic of Korea

We have explored a new mechanism for switchingmagnetism and superconductivity in a magnetically frustrated iron-basedsuperconductor using spin-polarized scanning tunneling microscopy (SPSTM) [1,2].Our SPSTM study on single crystal Sr2VO3FeAs made ofalternating self-assembled FeAs monolayer and Sr2VO3bilayers shows that a spin-polarized tunneling current can switch the FeAs-layermagnetism into a non-trivial C4 (2×2) order, which cannot beachieved by thermal excitation with unpolarized current. Our tunnelingspectroscopy study shows that the induced C4 (2×2) order hascharacteristics of plaquette antiferromagnetic order in the Fe layer andstrongly suppresses superconductivity. Also, thermal agitation beyond the bulkFe spin ordering temperature erases the C4 state. These resultssuggest a new possibility of switching local superconductivity by changing thesymmetry of magnetic order with spin-polarized and unpolarized tunnelingcurrents in iron-based superconductors [3,4]. We also performed high-resolutionquasiparticle interference (QPI) measurements, self-consistent BCS-theory-basedQPI simulations and a detailed e-ph coupling analysis to provide directatomic-scale proofs of enhancement of iron-based superconductivity due to theBCS mechanism based on forward-scattering interfacial phonons [5].

[1] Jin-Oh Jung et al., Rev. Sci. Instrum. 88,103702 (2017)

[2] Jhinhwan Lee, Rev. Sci. Instrum. 88, 085104 (2017)

[3] Seokhwan Choi et al., Phys. Rev. Lett. 119,227001 (2017)

[4] Dirk van der Marel, Physics 10, 127 (2017)

[5] Seokhwan Choi et al., Phys. Rev. Lett. 119,107003 (2017)

Fig. 1. (a)-(b) Atomic scale evidence of C4 antiferromagnetic order induced in FeAs layer of Sr2VO3FeAs by injection of spin-polarized tunneling current and (c)-(d) resultant local suppression of iron-based superconductivity [3]. (e)-(f) Spectroscopic evidences of local enhancement of iron-based superconductivity due to oxygen vacancies in VO2 layer (rice-shaped C2 defects in (e)) which locally enhance coupling of FeAs electrons with the forward-scattering interfacial phonons [5].